1. Field of the Invention
The present invention relates to a data comparison method and a data comparison apparatus for determining whether or not there is a match between an incoming data to be compared and any one of a plurality of registered data stored in a registered-data storing unit. More particularly, it relates to a method and an apparatus for comparing image data or feature data extracted from the image data with a plurality of registered image or feature data.
2. Description of the Prior Art
Referring now to FIG. 6, there is illustrated a block diagram showing the structure of a prior art data comparison apparatus. In the figure, reference numeral 1 denotes a registered-data storing unit for storing a plurality of registered data, 2 denotes a registered-data reading unit for reading the plurality of registered data sequentially, 3 denotes an additional information comparing unit for comparing an incoming data's additional information with one registered data's additional information, 4 denotes a comparison processing unit for comparing the incoming data's feature data with the registered data's feature data when the incoming data's additional information matches the registered data's additional information, and 5 denotes a comparison process skipping unit for skipping the comparison process when the incoming data's additional information does not match the registered data's additional information.
In operation, each time the registered-data storing unit 1 receives one data to be registered, it stores the data. When the prior art data comparison apparatus receives an incoming data (or target data) to be compared, the registered-data reading unit 2 sequentially reads the plurality of registered data one by one from the registered-data storing unit 1. The additional information comparing unit 13 then compares the additional information of one registered data read by the registered-data reading unit 2 with the additional information of the incoming data to be compared. When the registered data's additional information matches the incoming data's additional information, the comparison processing unit 4 compares the registered data's feature data with the incoming data's feature data so as to obtain the degree of match between the registered data's feature data and the incoming data's feature data. The comparison processing unit 4 then instructs the registered-data storing unit 2 to read the next registered data. In contrast, when the registered data's additional information does not match the incoming data's additional information, the comparison processing skip unit 5 skips the comparison process that would be carried out for the registered data just read out of the registered-data storing unit 1, and then instructs the registered-data reading unit 2 to read the next registered data. In this manner, the incoming data to be compared is sequentially compared with all of the plurality of registered data stored in the registered-data storing unit 1.
Round-robin comparing an incoming data to be compared with the plurality of registered data and determining that the incoming data matches one registered data showing the highest degree of match are concepts behind the prior art data comparison apparatus mentioned above. Since much time is required to carry out round-robin comparisons, the time required for the comparison process can be reduced by skipping the comparison between the target data to be compared and one registered data whose additional information does not match the target data's additional information, as mentioned above. For example, in the case of comparison of fingerprints, each of an incoming data and a plurality of registered data is constructed of feature data such as features of a corresponding fingerprint, and information about the pattern of the fingerprint is added (fingerprints are classified into some groups according to their patterns), as additional information, to the feature data. The prior art data comparison apparatus compares the target data with each of the plurality of registered data with respect to their additional information first, and then skips the comparison process for their feature data unless there is a match between the target data's additional information and each registered data's additional information.
Japanese Patent Application Publication (KOKAI) No. 7-29003 discloses such a prior art data comparison apparatus, for example. In the reference, there is disclosed a fingerprint comparison (or identification) apparatus in which additional information associated with the feature data of an incoming fingerprint and additional information associated with the feature data of each of a plurality of registered fingerprints are stored and a process of comparing the incoming fingerprint data with one registered fingerprint data whose additional information does not match the incoming fingerprint data's additional information is skipped.
A problem with the prior art data comparison apparatus so constructed as mentioned above is thus that since the prior art data comparison apparatus carries out round-robin comparisons between an incoming data to be compared and all registered data, much time is needed for the comparison processing. Another problem is that if there is an error in the additional information added to any feature data, the process of comparing the feature data with the feature data of the incoming data to be compared is skipped after the comparison between the additional information added to the feature data and the incoming data's additional information even though the feature data is similar to the feature data of the incoming data to be compared. For example, in the case of fingerprint data, information about the pattern of the fingerprint is added, as additional information, to the fingerprint data in most cases. An error can occur in the classification of the pattern of the fingerprint. If there is an error in the classification of the pattern of a registered fingerprint, the process of comparing the feature data of the registered fingerprint with the feature data of an incoming fingerprint whose additional information differs from the registered data's additional information is skipped, after the comparison between the registered data's additional information and the incoming data's additional information, even though the registered fingerprint feature data is similar to the feature data of the incoming fingerprint to be compared, as mentioned above. Accordingly, there is a possibility that a registered data that actually matches the incoming data to be compared is not selected and it is then determined that another registered data matches the incoming data, and therefore a desired registered data, such as a desired fingerprint, cannot be extracted.